1. Field of Invention
The present invention relates to a semiconductor device, and particularly to a light emitting diode chip (LED chip).
2. Description of the Related Art
A light emitting diode (LED) is a semiconductor device, and the material of the emitting chip is usually chemical elements of group III, group IV and group V, namely compound semiconductors, such as gallium phosphide (GaP), gallium arsenide (GaAs) and gallium nitride (GaN). Applying current to the compound semiconductors by means of recombination of electrons and holes, the electric energy is converted into optic energy and released in photon form to achieve light radiation. The light radiation of an LED is belonged to the so-called “cool light radiation”, rather than radiated by heat, therefore, the lifetime of an LED can be over a hundred thousand hours without any idling time. In addition, an LED has advantages such as fast response speed (about 10-9 second), small volume, electricity saving, low pollution (mercury free), high-reliability and adaptable to mass production. Hence, LEDs are widely used in many fields, such as light sources of scanners, backlight sources of LED screens, outdoor display boards or vehicle lightings.
FIG. 1A is a schematic top view of a conventional LED chip and FIG. 1B is a schematic cross-sectional drawing taken along section plane A-A′ in FIG. 1A. Referring to FIGS. 1A and 1B, a conventional LED chip 100 includes a substrate 110, an N-type doped semiconductor layer 120, a light emitting layer 130, a P-type doped semiconductor layer 140, an N-type electrode 150 and a P-type electrode 160. The N-type doped semiconductor layer 120 is disposed on the substrate 110, the light emitting layer 130 is disposed on the N-type doped semiconductor layer 120 and the P-type doped semiconductor layer 140 is disposed on the light emitting layer 130. The N-type electrode 150 disposed on the N-type doped semiconductor layer 120 comprises a first bar-like pattern 152 and a plurality of first branches 154, while the P-type electrode 160 disposed on the P-type doped semiconductor layer 140 comprises a second bar-like pattern 162 and a plurality of second branches 164.
In addition, the first bar-like pattern 152 is opposite to the second bar-like pattern 162; the first branches 154 are connected to the first bar-like pattern 152 and located at a side of the first bar-like pattern 152. The second branches 164 are connected to the second bar-like pattern 162 and located at a side of the second bar-like pattern 162. The first branches 154 and the second branches 164 are alternately arranged to each other.
When the N-type electrode 150 and the P-type electrode 160 apply a forward current to the LED chip 100, the electrons and the holes are transmitted to the light emitting layer 130 from the N-type doped semiconductor layer 120 and the P-type doped semiconductor layer 140, respectively, and are recombined there so as to release energy in photon form and radiate light.
Note that the N-type electrode 150 and the P-type electrode 160 herein take open-loop form, therefore if the N-type electrode 150 or the P-type electrode 160 was broken accidentally (as shown at area 50 in the figure), a part of the LED chip 100 would be an electric open-circuit. Consequently, a partial region of the light emitting layer 130 would not radiate light, which reduces the luminous efficiency of the LED chip 100. In particular, the larger the size of the LED chip 100, the more serious the negative effect on the luminous efficiency from the broken N-type electrode 150 or P-type electrode 160 is. Furthermore, for a larger-sized LED 100 in the prior art, a total internal reflection (TIR) of the light emitted from the light emitting layer 130 inside the LED 100 is more remarkable, which would further deteriorate the luminous efficiency of the LED chip 100.